Open ocean shallow water moor

ABSTRACT

An open ocean moor is disclosed for use at comparatively shallow ocean depths. The moor consists of a buoy floating on the surface which is fastened to an anchor on the bottom by means of a flexible tether formed of a plurality of linked sections of highly elastic material such as rubber of relatively large crosssectional area. The elastic sections are formed with heavy loops or eyelets at each end, and adjoining sections are connected by means of a link formed of two mating double grommet assemblies which, preferably, are also formed of mating configuration with respect to the loops to minimize stress concentrations. An electrical cable which is connected to various underwater instruments extends from the buoy to the anchor. This cable is supported on the flexible tether line by means of separate cable clamps on the links. A substantial amount of slack must be maintained in the electrical cable to allow for stretching during periods of high wave action without danger of pulling the cable taut. The electrical cable is fastened to the anchor and to the buoy by means of cable termination devices of a type known in the art.

United States Patent [191 Horrer et a1.

[451 July 3,1973

[ OPEN OCEAN SHALLOW WATER MOOR [75] Inventors: Paul L. Horrer, LaJolla; Robert M.

Bridges, Northridge, both of Calif.

[73] Assignee: The Bendix Corporation, Southfield,

Mich.

221 Filed: Mar.31, 1971 21 Appl. No.: 129,716

Primary Examiner-Duane A. Reger Assistant Examiner-Gregory W. OConnorAtlorney-Robert C. Smith and Flame, Hartz, Smith & Thompson [5 7]ABSTRACT An open ocean moor is disclosed for use at comparativelyshallow ocean depths. The moor consists of a buoy floating on thesurface which is fastened to an anchor on the bottom by means of aflexible tether formed of a plurality of linked sections of highlyelastic material such as rubber of relatively large crosssectional area.The elastic sections are formed with heavy loops or eyelets at each end,and adjoining sections are connected by means of a link formed of twomating double grommet assemblies which, preferably, are also formed ofmating configuration with respect to the loops to minimize stressconcentrations. An electrical cable which is connected to variousunderwater instruments extends from the buoy to the anchor. This cableis supported on the flexible tether line by means of separate cableclamps on the links. A substantial amount of slack must be maintained inthe electrical cable to allow for stretching during periods of high waveaction without danger of pulling the cable taut. The electrical cable isfastened to the anchor and to the buoy by means of cable terminationdevices of a type known in the art.

8 Claims, 4 Drawing Figures OPEN OCEAN SHALLOW WATER MOOR BACKGROUND OFTHE INVENTION There are many applications for bottom-mounted moors thattether a buoy in place on the surface of the ocean. For oceanographicstudies, it is frequently desired toplace instruments in the ocean whichwill provide readings of underwater temperatures, current flow, etc.,which readings are converted to electrical signals and which must thenbe brought to a buoy on the surface and relayed through radio means inthe buoy to shore stations. Where such buoys are moored in very deepwater (of the order of 10,000 feet or more), it has been establishedpractice to tether the buoy to the moor by means of a very strong, butsomewhat elastic, connection such as a nylon rope. This rope willnormally be tensioned to some extent, even in calm seas, to avoidgenerating slack and then sudden tightening which would result inexcessive wear on the rope. In the case of very heavy seas, wave heightsof the order of 100 feet are possible and should be planned for. In thecase ofa very deep moor, this would involve a stretching of the nylonrope by an amount even including some lateral displacement of the buoy,which is actually a very small percentage of the length of theunstretched rope. The nylon ropes which have been used for this purposeeasily accommodate this kind of stretching, and the buoys usually rideout heavy seas without any damage. Where it has been desired to locateinstruments in relatively shallow water, however, a much more difficultyproblem is presented. By shallow water, in this instance, is meant waterof the normal depth on the various continental shelves and which mightbe of the order of 600 feet or less. Even in water of this depth, severestorm conditions can result in waves of the same height as that of theopen sea or nearly so, and therefore it again becomes necessary todesign for l-foot wave action. Given this relationship and the lateraldisplacement of the buoy which occurs in severe storms, it now becomesnecessary to deal with a mooring means which may need to stretch up to2% times its length rather than, perhaps, one onehundredth or onefiftieth, as in the case of the deep water moor previously referred to.This percentage of elongation is not within the capability of thetypical nylon rope used in connection with deep water moors. Since suchmoors should be designed for a minimum life of one year irrespective ofthe weather conditions encountered, it will be recognized that thousandsof elongation cycles must be withstood for acceptable life. In additionto withstanding the very substantial stretching required, the cablematerial must be stable in sea water for the requisite period of time,and it must have a spring rate sufficient to adequately support theconductor carrying the instrumentation signals to the buoy. 1

The means for attaching the tethering structure to the anchor, to thebuoy, and to the electrical cable also becomes very important in thisapplication. It will be apparent that sufficient slack must be placed inthe electrical cable so that it does not become taut and accept mooringstresses during operation in this adverse environment. If the lattercondition should occur, the moor will rapidly destroy itself by veryhigh loads delivered through the cable into the buoy and the anchor.

It can be seen that it is important that all parts of the tetherassembly he as lightweight as possible to reduce the amount of supportedload and consequently the amount of prestretch of the elastic mooringmember. The amount of supported weight is affected by the amount ofstretch designed into the elastic member, since its design is governedby the loads placed on the buoy, wave motion and downward forces of thetether, plus cross-current forces on the tether assembly. Stretch,therefore, must not be excessive since slack in the electrical cable isdetermined by the maximum amount of stretch permitted in the elastictether membet.

The spring rate of the elastic member is significant since enoughstretch must be designed into the elastic member to allow for theorbital motion of the surface buoy on the surface as it follows the wavein addition to the static stretch produced by wind forces on the buoyand current forces on the tether assembly. This design considerationplaces a maximum constraint on the spring rate while the supportedweight of hardware and electrical cable places a minimum constraint onthe spring rate (i.e., excessively long stretch results in excessivelylarge cable weights).

Since it is impractical to mold a rubber or rubberlike tether member ofseveral hundred feet in one piece, and also because it is necessary toattach the electrical cable at several points along the tether, meansmust be supplied for linking the tether sections together as well assupporting the cable at various points. Such link means should bedesigned to avoid concentrated stress on the ends of the tethersections.

SUMMARY OF THE INVENTION By means of this invention, a mooringarrangement is provided which includes a plurality of elongated elasticmembers which are terminated at each end in eyelets of substantialthickness and strength. These are tied together through lightweightlinks in the form of double grommet assemblies which are bolted togetherto contain the eyelets. Also fastened to the links are separate cableclamp means which secure the electrical cable to the flexible tetherline. Preferably, the grommet assemblies include mating spacer portionswhich, when bolted together, produce a support of mating configurationfor the eyelets to thereby equalize the stress on the eyelets duringsevere stretching.

A certain amount of preload is introduced in the tether assembly so thatin calm seas the load of the cable assembly, the mounting link and theweight of the elastic members can be supported without producing slacknear the anchor which could result in kinking or twisting of theelectrical cable with resulting fatigue and possible failure. Thus thespring rate or stiffness must be such as to supply this support, whileat the same time it must not be so stiff as to cause the buoy to besubmerged in heavy weather.

The electrical cable is attached at each link and must have substantialslack between the links to accommodate the stretching of the elasticmember. This cable is sufficiently strong to carry a substantial load intension but must not be exposed to the shock which would occur if itwere to be repetitively snapped taut and loose because its length wasinsufficient to tolerate the maximum wave action experienced. Because ofthe slack in the cable, it is necessary that it be protected againstextreme bending angles at the upper side of each attachment link. Thisprotection has been provided by means of a wire rope support meansfastened as a sleeve at each link which stiffens the cable at that pointto limit the radius of curvature which it can experience.

The buoy which is tethered may be of a type which has a weathervaneaction, thus seeking always to be headed into the wind. To attach thecable to such a buoy requires that a swivel mechanism, which may includeelectrical slip rings, be used to prevent twisting of the cable and thetether line. This cable is then fastened to the swivel through a cabletermination device. A similar termination device is used to attach thecable to the anchor.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawing showing atypical open ocean shallow water moor according to my invention;

FIG. 2 is a side plan view showing the elastic tether sections, theelectrical cable and the linking devices for connecting said sectionsand for attaching the electrical cables to the tether;

FIG. 3 is an enlarged top plan view, with the center broken away, of oneof the elastic tether members shown in FIG. 2; and

FIG. 4 is an enlarged side plan view, in partially exploded form, of thelink and cable clamp arrangement shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT A typical open ocean, shallowwater buoy for gathering underwater data and transmitting the datathrough radio means to shore stations is shown in FIG. 1. Variousunderwater instrumentation devices 10, 12 and 14 are attached to anunderwater electrical cable 16 which is supported at some substantialdistance off the ocean bottom by means of a float 18 anchored to thebottom by means of an anchor 20. Cable 16 is fastened to anchor 20 bymeans of a cable termination device 22 which may be of the type shown inMaddux US. Pat. No. 3,288,913 and which is tied to a lug 21 on anchor20. Cable 16 then extends along the bottom to a second anchor 24 whichhas attached to it a similar cable termination device 26. The cable 16passes through the cable termination device 26 which is otherwiseattached to a lug 28 on the anchor 24. It will be observed that cable 16extends a short distance from the termination structure 26 and then isclamped into a link 30 which includes a double grommet structure forattach ing one end of a flexible tether section 32. The opposite end oftether section 32 is attached to a similar link 34 which also includes acable clamp means supporting cable 16. A number of identical tetheringlinks, including members 36, 38 and 40, are tied together and to cable16 by means of link members 42, 44 and 46. Obviously, many more sectionswill normally be involved in spanning a depth of 500 or 600 feet. Cable16 is supported by clamp means at each of the links in such manner as toretain a substantial amount of slack in the electrical cable in quietweather. At the upper end, cable 16 is attached to the floating buoy 48by means of an additional cable termination device 50 which may besimilar to devices 22 and 26. The buoy 48 will normally containelectronic equipment for transmitting electrical signals received fromthe instrumentation devices 10, 12 and 14 to shore stations.

FIG. 2 shows a typical length of electrical cable and the supportingflexible tether sections which are attached together through the use ofthe link members, as described. This figure shows, in somewhat greaterdetail, the structure of the individual elements and the manner in whichthey are assembled to provide the desired flexible moor device. A link30 which corresponds to the link of the same number shown on FIG. 1 isattached through cable 16 to the cable termination device 26 as shown inFIG. 1 and provides a clamp for the electrical cable 16. This clamp alsosupports a somewhat stiff wire rope sleeve 52 which is of taperedstiffness to support cable 16 in such a way that its radius of curvatureleaving the link member is limited so that it cannot bend back sharplyon itself. The loop at one end of the flexible tether member 30 issecurely positioned between the bolted-together halves of the link 30which form a spool-like structure which is of mating configurationrelative to the inside of the loop in order to minimize the stressconcentrations on the loop. Link 44 connects two such flexible tethermembers 38 and 40 and also supports a section of cable 16 in the mannerdescribed and also secures a sleeve member 54 to preventa sharp bendingof the cable. Flexible tether member 40 is terminated at link 46 andcable member 16 passes through the clamp and the termination 50 and tothe buoy 48. It will be recognized that with this arrangement there willbe substantial tension load on the cable 16 below link 30 and above link46, but with the flexibility imparted by the flexible tether members32-40, etc., this tension load will be essentially continuous and notsubject to sudden release and reapplication with corresponding danger ofkinking or buckling. Should a limited number of flexible tether membersbreak in operation, the corresponding cable sections will receive atension load, but there will be sufficient compliance remaining in thetether to handle large wave action.

FIG. 3 is a plan view, with a portion of the center broken away, of atypical elastic tether member. Each of these members is essentially likemember 32 and is formed with large loops or eyelets 32' and 32" at eachend. The diameter of the rubber material in the eyelet is essentiallythe same as that in the center of the member. Although there wouldnormally be a considerable degree of latitude in this respect, thelength of the tether members used by applicant was approximately 16feet. The use of unduly long lengths would load the connecting linksexcessively because of the amount of slack cable to be supported. Thediameter or thickness of the center section used was approximately 1%inch. This thickness, of course, is controlled by the spring raterequired for a given application. The diameter of the eye of the loopwas approximately the same as the diameter of the rubber member, or 1%inches. Again, this dimension may vary, depending upon loadingconditions. Initial attempts to produce a flexible tether member of thistype involved the use of a member having a round cross-section andflattened on the ends so that they could be drilled and bolted to a linkor splicing member. As a result, forces were concentrated around thearea where the bolt penetrated the flexible member and the connectionfailed because the bolt ultimately pulled out through the flattenedportion of the rubber member. The present design is much superior andhas withstood hundreds of thousands of elongations of 2 to 2% times itsunloaded length. Applicant's members 32 were made of natural rubber andwere not molded with reinforcements of any type built into the endloops. Under tension, the rubber flows smoothly around the support whichpasses through the eye of the loop andis able to withstand verysubstantial loads.

FIG. 4 shows a plan view, partially exploded, of the link structure usedfor tying together the individual tether sections and also for clampingthe electrical cable 16 to the tether. Since the link member is the sameas that shown in FIG. 2 at numeral 44 (as well as the several others),it will be considered an enlarged view of the structure 44. The tethermembers 38 and 40 are identical to those shown in FIG. 3 and are tiedtogether by means of the link member 44 which consists of two matingdouble grommet members 56 and 58 having side plates which contain theend loops of elastic tether members 38 and 40. These members should beof lightweight material chosen to withstand the sea water environment,and may be any of several plastics. Member 56 has attached thereto ablock 60 which cooperates with a mating block 62 to form a clamp forsupporting and restraining the electrical cable 16 and its supportingsleeve 54. Each of the double grommet members 56, 58 includes a pair ofmating grommet sections 64, 66 which are in the shape of a low filletedcylindrical attachment to the corresponding plate, and each is drilledas at 68 and 70 to receive a through bolt 72, 74, respectively. It willbe observed that the grommet section 66 includes an upstanding collar 76which mates with a corresponding depression 78 in the adjoining grommetsection. This, of course, preserves the alignment between the matinggrommet sections as the nuts 80 and 82 are tightened on the bolts 72 and74, respectively. Clamping plates 60 and 62 are also drilled toaccommodate a plurality of other bolts 84 which are threadedly engagedwith plate 60 to secure the cable 16 and sleeve 54 to the link 44. Itmay be desired to safety-wire these bolts as shown at numeral 86 toassure their remaining secured in operation.

It will be apparent to those skilled in the art that modifications maybe made, depending upon the requirements of individual installations.Thus, while applicant has shown a specific manner in which theelectrical instrumentation is deployed, other means may be used. While agiven type of cable termination is shown and described, there are othertermination arrangements which would be operative in this type ofinstallation.

It will be apparent to those skilled in the art that modifications maybe made, depending upon the requirements of individual installations.Thus, while applicant has shown a specific manner in which theelectricalinstrumentation is deployed, other means may be used. While a given typeof cable While applicants have shown elastic tether members of circularcross-section and a given size has been discussed, both size andcrosssectional configuration are subject to change depending uponrequirements. For instance, a cross-section in the form of a roundedsquare would be quite feasible for this purpose and might be used bothin the main center section of the tether member as well as in the endloops. Depending upon the thickness and weight of the electrical cable16 used, the sleeve structure for limiting the radius of curvature mayor may not be required. There are a number of advantages to using thekind of buoy which has a weather vane action and which, therefore, tendsalways to turn into the wind action. This makes a swivealable connectionat the buoy a mandatory requirement to avoid excessive twisting of thecable and tether. Another type of buoy which is not so subject torotation may permit a less flexible type of connection between the cableand the buoy.

We claim:

1. An open ocean shallow water moor comprising a buoy;

an anchor on the ocean floor;

means generating electrical signals to be transmitted to said buoy;

an electrical cable for connecting said signals from said means to saidbuoy;

and a tether assembly for attaching said buoy to said anchor and forsupporting said electrical cable, said assembly comprising a pluralityof elongated elastic members of substantial thickness each of which iscapable of being stretched to at least a substantial percentage greaterthan its unstretched length over a large number of cycles, said membersbeing formed such that they terminate at each end in an eyelet ofsubstantial thickness; and

a link for attaching saidelastic members together including a doublegrommet member formed with side plates and spacers such that, when saidmembers are fastened together, support posts are formed of said spacersand said eyelets are contained on said posts;

and cable clamp means fastened to one of said plates.

2. An open ocean shallow water moor as set forth in claim 1 wherein saidspacers are mating parts which, when fastened together, form supportposts which substantially flll said eyelets and generally conform to theshape of said eyelets.

3. An open ocean shallow water moor as set forth in claim 2 wherein saidelastic member and said eyelets are of essentially round cross-section.

4. An open ocean shallow water moor as set forth in claim 1 wherein thethickness of said elastic members is such as to produce a spring ratepermitting the buoy to follow wave action while adequately supportingitself, said electrical cable and said links.

5. An open ocean shallow water moor as set forth in claim 4 wherein saidtether assembly has a tension preload, even in quiet water, sufficientto prevent substantial slack in said electrical cable immediately abovethe said anchor.

6. An open ocean shallow water moor as set forth in claim 1 wherein saidelectrical cable is fastened to said cable clamp means such that saidcable has sufficient slack between each of said clamp means that it doesnot pull taut at the maximum wave amplitudes experienced.

7. An open ocean shallow water moor as set forth in claim 1 whereinsupport meansis provided at each of said cable clamp means to limit theradius of curvature of said electrical cable upwardly of said clampmeans.

8. An open ocean shallow water moor as set forth in claim 1 including anunderwater float, a second anchor, means attaching said float to saidsecond anchor, and wherein said electrical signal-generating means issuspended from said float.

1. An open ocean shallow water moor comprising a buoy; an anchor on theocean floor; means generating electrical signals to be transmitted tosaid buoy; an electrical cable for connecting said signals from saidmeans to said buoy; and a tether assembly for attaching said buoy tosaid anchor and for supporting said electrical cable, said assemblycomprising a plurality of elongated elastic members of substantialthickness each of which is capable of being stretched to at least asubstantial percentage greater than its unstretched length over a largenumber of cycles, said members being formed such that they terminate ateach end in an eyelet of substantial thickness; and a linK for attachingsaid elastic members together including a double grommet member formedwith side plates and spacers such that, when said members are fastenedtogether, support posts are formed of said spacers and said eyelets arecontained on said posts; and cable clamp means fastened to one of saidplates.
 2. An open ocean shallow water moor as set forth in claim 1wherein said spacers are mating parts which, when fastened together,form support posts which substantially fill said eyelets and generallyconform to the shape of said eyelets.
 3. An open ocean shallow watermoor as set forth in claim 2 wherein said elastic member and saideyelets are of essentially round cross-section.
 4. An open ocean shallowwater moor as set forth in claim 1 wherein the thickness of said elasticmembers is such as to produce a spring rate permitting the buoy tofollow wave action while adequately supporting itself, said electricalcable and said links.
 5. An open ocean shallow water moor as set forthin claim 4 wherein said tether assembly has a tension preload, even inquiet water, sufficient to prevent substantial slack in said electricalcable immediately above the said anchor.
 6. An open ocean shallow watermoor as set forth in claim 1 wherein said electrical cable is fastenedto said cable clamp means such that said cable has sufficient slackbetween each of said clamp means that it does not pull taut at themaximum wave amplitudes experienced.
 7. An open ocean shallow water mooras set forth in claim 1 wherein support means is provided at each ofsaid cable clamp means to limit the radius of curvature of saidelectrical cable upwardly of said clamp means.
 8. An open ocean shallowwater moor as set forth in claim 1 including an underwater float, asecond anchor, means attaching said float to said second anchor, andwherein said electrical signal-generating means is suspended from saidfloat.